1. Field of the Invention
This invention relates to a display device with an optical input function which can input information by, for example, causing light from a light source such as a light pen to illuminate the display screen. With the display device, illuminated position information or contact position information on the display screen illuminated by the light is detected. More specifically, this invention is made clearer by explaining embodiments to be described later.
2. Description of the Related Art
Recently, a liquid crystal display device is widely used as a display device for various equipment such as a mobile telephone or notebook-sized personal computer. The liquid crystal display device is configured by an array substrate on which liquid crystal pixel portions including thin film transistors (TFT), liquid crystal capacitors and auxiliary capacitors are arranged at intersecting portions between a plurality of scanning lines and a plurality of signal lines, and a drive circuit which drives the scanning lines and signals lines. However, recently, with the development of integrated circuit technology and practical implementation of improved processing techniques, part of the drive circuit is also formed on the array substrate and an attempt is made to reduce the liquid crystal display device in size and weight.
On the other hand, a display device in which a contact type area sensor having an image fetching function is arranged on an array substrate is proposed as a display device having an optical input function. The conventional display device of this type having the optical input function includes display means configured by, for example, liquid crystal pixel portions arranged at intersecting portions between a plurality of scanning lines and a plurality of signal lines and photosensing means formed of photodiodes, for example. In the photosensing means, the amount of charges of capacitors connected to the photodiodes varies according to the amount of light received by the photodiodes. Therefore, the display device can fetch an image since image data can be formed by detecting voltages across a plurality of capacitors at the intersecting portions.
With the display device having the optical input function, a method for attaining multi-gradation image data corresponding to the illumination intensity of incident light based on image data obtained in a plurality of image photographing conditions by an image processing operation is proposed.
Further, a method for fetching an image while an image is being displayed by inserting an image photographing frame between display frames which are used to display an image is proposed. By using the above method, for example, a pen-type light source can be used as a coordinate input device of the display device by illuminating the display screen by use of the pen-type light source. A coordinate calculation algorithm or tap detecting algorithm used to serve the above purpose is proposed (refer to Jpn. Pat. Appln. KOKAI Publication No. 2002-182839, for example).
(A1)
In the conventional display device having the optical input function, since image data having dot-form defects or line-form defects caused and generated in the manufacturing process is output to the exterior as it is, it becomes necessary to perform an image processing operation which compensates for the defects by use of an external IC. In order to perform the image processing operation, it is generally required to provide a memory with a storage capacity corresponding to several lines of image data in the IC, and therefore, there occurs a problem that the circuit scale of the IC becomes large and the cost thereof becomes high.
If the compensation process is not performed by use of the external IC, it becomes necessary to select and use only a display device having an optical input function which is free from the defects. As a result, there occurs a problem that the manufacturing yield is lowered.
(B1)
Further, in the display device having the optical input function, for example, when coordinates are input by illumination by use of a light source such as a light pen, there occurs a problem that it is difficult to determine whether or not the tip end of the pen is set in contact with the display screen since the light source is always kept ON. In order to solve the above problem, a method for determining the contact/non-contact state by attaching a switch to the tip end of the pen and turning ON the light source only at the contact time may be considered. However, with this method, it is difficult to realize smoothly writing feelings.